Hello,I'm hoping someone might be able to help me find this cooling gremlin I've been fighting for ages after a top end rebuild.The top end rebuild was done on my pontiac 455, including new PRW water pump, power steering, alternator, HEI distributor, and 3 core aluminum radiator with 2x 12' electric fans in my 73 Trans Am.Immediately after the top end rebuild, it runs at about 210 while idling and driving on city streets indefinitely, and will fluctuate up to 230 while on the highway that doesn't have a grade or is downhill. If the highway is uphill, then it will easily hit 250 after about 5 minutes. There also seems to be more condensation in the exhaust than should be there, but no milky oil. I have tried:Pressure testing cooling system: It loses 50psi after 30 minsCompression test: all cylinders were between 155-165Leak down test: 10%Smoke test shows no hydrocarbons in the cooling system (no blown head gasket)Liquid block test shows no combustion getting into the cooling systemWater pump is high performance PRW, can confirm it is moving coolantTiming adjustments to various configurationSwapping spark plugs: autolite version of the 7587Swapping thermostat various temps between 160-180change back to mechanical fan + shroudAdding water wetterreplaced coolant temp sending unitAdditionally, the gauges are showing strange behaviors. My voltmeter seems to be reporting low voltage (fluctuating between 11-13) at RPM's above 2200, and the water temp seems to fluctuate along with the voltage. When the voltage is low (11), the water temp climbs to 230. When the voltage is good 13-14, the temp falls back to 210. I cannot understand how these things can be related since this is at a highway speed, so the fans are the only part of the cooling system that pulls electricity and not a necessary part of the cooling system on the highway. Why would low voltage and high temperature be related? Specs:Cam: Tomahawk Hydraulic Cam 274/280 Dur@.050 224/232 Lift@1.5 480/485 LC 112 #TC-01-HFHeads: 6s-9 (101cc combustion chamber)Transmission: 350 / 3.08 gearsBore size .40 overHEI Distributor: 11 degrees initial , 33 degrees total, and its all in at around 2500, not picking up pinging. (have tried up to 14 degrees as well)
My first thought is to temporarily try a mechanical gauge (with sensor in intake manifold) to confirm that a problem exists. Second thought is: "loses 50 psi after 30 mins" is lot of pressure. I don't think I would want to put more than half that pressure on the system, myself. But any leak means the system cannot pressurize or cool properly so I would look into that, too. Even a heater core leak that only passes air but doesn't show a coolant trail. Did you check the cap, too? The .040 over on a 455 is about max. Last time I tried a fresh top end on an unknown poked bottom end, I found out about thrust side bore wear. That one acted kinda like yours but was bleeding coolant.
I would get a infrared thermometer gun and check some spots , hoses , rad , block , and see if you really have a problem .
Additionally, the gauges are showing strange behaviors. My voltmeter seems to be reporting low voltage (fluctuating between 11-13) at RPM's above 2200, and the water temp seems to fluctuate along with the voltage. When the voltage is low (11), the water temp climbs to 230. When the voltage is good 13-14, the temp falls back to 210. I cannot understand how these things can be related since this is at a highway speed, so the fans are the only part of the cooling system that pulls electricity and not a necessary part of the cooling system on the highway. Why would low voltage and high temperature be related? open the hood and perform this voltage drop test.. ######################why... because the ground side is half the circuit..the temp gauge is only hooked up with ONE wire.. where is the other half of the circuit.. the block.. but the block sits on rubber mounts.. the braided ground strap from the back of the cylinder heads to the firewall is the best connection. thats tested on test 4.. bet you find more than the 2/100ths of a volt when you run the tests..let me go farther..the battery has 12.65 volts at full charge..the alternator puts out 14.1 or a little more.. but it puts it out on the Negative side.. electrons want to take the shortest path.. since there is more voltage on the block than there is from the battery.. the electrons will flow from the block to the body via the ground strap.. if that ground strap is missing.. the electrons will have to go the LONG way around.. up the negative cable.. to the battery terminal.. to the small wire to the inner fender. then thru the fender to the main shell of the body .. before it gets to the firewall..i would also like you to perform tests 1 and 2 while cranking the engine..post results..1.____2.____3.____4.____while cranking.. min max buttons on the volt meters work great for this.. 1 cranking.____ 2 cranking.____the image above of the tests should be printable.. its a JPG. drag it to your desktop..
Several items come to mind on this one, the key phrase being, top end rebuild.Start with the gauge issue potential, start with checking to be sure you have a good ground that was on the right head to the firewall. Next check to be sure the engine is getting to hot, as suggested using a temp probe. If you can't stand to put your hand on the valve cover, its to hot. Extreme heat can effect the alternator but not likely due to the battery will still read at least 12v-14v without the alternator, check the ground.Next, back in the early 70s GM retarded the timing with the crank gear, so when you install a new timing gear set, you may have got a retarded gear, it's off about 1/2 tooth from the early ones, flop it over and grind a chanfer on the other side to fit the radius on the crank, this will give you the advanced gear, of course if you kept the same gear this will not be the case.You can check it against the old one, lay one on top of the other, line up the keyway and look at the gear, if they're not the same, flop the new one over and stack them again then you'll understand what to do.This can make it heat up quick and run hot, also makes it hard to set the timing to where it needs to be. GTO guy
+1 on everything advised above.One other thing, your electric fans may be hindering more than helping. They can retard air flow as much as help. Other's have come to this forum with over heating problems using electric fans. Our recommendation was to go back to a factory set up with 7 blade fan/clutch set up, or similar and that has either cured their problems or greatly reduced their operating temps. also, make sure your fan shroud is in good condition.
Thanks guys.Ok first step is to verify that there is actually a problem. It's been a really long time since it actually boiled over and I've tried very hard to not let it get to that point, so I don't have a ton of recent evidence (i've only put a few hundred miles on it since the rebuild, almost all of it troubleshooting this).wayne712222:I'm going to have an electrical shop look into the electrical system for me to verify the gauges, any potential voltage drop or electrical gremlins. I had a manual switch for the electric fans, so I'm also having him hook it up to a relay (i tried and didn't do a great job). So, that is being done today. Any suggestions for him to look into other than the voltage drop test are welcome.I'm going to add an additional mechanical gauge (want to keep the dash gauge so I can see the differences to gain confidence in it). There are 2 plugs on top of the intake manifold. One is being used for the temp gauge, the other for the fan relay. There are other places for plugs to go on the side of the intake manifold. Does it matter which one I use for the temporary mechanical gauge?I have an infared temp gun. I will hit: a. Radiatorb. Bottom Hosec. Water pumpd. Thermostat housinge. Top hose at radiatoridrivejunk:"loses 50 psi after 30 mins". Sorry, I typed that wrong, it's only 5psi after 30 mins."Even a heater core leak that only passes air but doesn't show a coolant trail."Heater coil is bad, and I've bypassed it. What is the proper way to bypass? "Did you check the cap, too?" Do you mean the radiator cap for the pressure release?"The .040 over on a 455 is about max. Last time I tried a fresh top end on an unknown poked bottom end, I found out about thrust side bore wear. That one acted kinda like yours but was bleeding coolant. " Any ideas on how to diagnose this?"Next, back in the early 70s GM retarded the timing with the crank gear, so when you install a new timing gear set, you may have got a retarded gear, it's off about 1/2 tooth from the early ones, flop it over and grind a chanfer on the other side to fit the radius on the crank, this will give you the advanced gear, of course if you kept the same gear this will not be the case.You can check it against the old one, lay one on top of the other, line up the keyway and look at the gear, if they're not the same, flop the new one over and stack them again then you'll understand what to ***So, what you are saying kinda scares me. When the top end was rebuilt, a comp cams roller timing chain set was used. I don't have the part number unfortunately, but the last thing I'm going to do myself is grind anything internal or that moves with other parts. Can you explain this in more detail?My71"One other thing, your electric fans may be hindering more than helping."I initially had this problem with the stock shroud and fan, and it hasn't changed significantly between the electric fans and the more stock setup. I would have to purchase new fan+shroud to test this so I think I'm going to hold on this as a troubleshooting step for now.Thanks again for helping me on this.
scrambler.. do you own a digital volt meter???this test only takes about 5 minutes for you to perform.. or.. stop by almost any parts store.. look out on the HELP display for this ground strap.. bolt it from the back of one of the cylinder heads to a good metal spot on the firewall.. this is about 6 bucks at most parts stores..i know automotive electrications.. they like to change parts.. this will probably if you get it hooked up properly.. solve your issue with gauge fluctutaions..
"loses 50 psi after 30 mins".Sorry, I typed that wrong, it's only 5psi after 30 mins."Ah, much better. Still a leak, but after half an hour thats pretty good I think. Maybe not perfect but good."Heater coil is bad, and I've bypassed it. What is the proper way to bypass?"I don't like to run that way, it reduces the total coolant capacity. But if as in your case, its toast, I use a plastic reducing nipple and connect the two hoses. I keep one with a couple clamps in the glovebox for just that occasion.A word or two about the heater hose nipple in the head ... thats a sneaky spot for a leak, or air seepage. I like to use a small amount of sealant when driving that in. The stock type part (GM might still sell them) is a stamped press fit design and has a heater core pressure spike-protecting bimetal spring inside. I have also seen them with just a reduced I.D. in the nipple. A leak there goes straight down the back of the engine and may dry up before it hits the ground or accumulates. Pressurize the system and try soapy water there? Even a pinhole in a heater hose could do it because being the highest point in the system, thats where air goes. On to the next thought I had. Wasn't sure if the others had touched on this but the water pump divider plate clearance can cause your scenario if it is excessive. I do recall you said you have an aftermarket pump. A little fussing over your existing parts might solve it if thats the case. The metal plate behind the water pump needs to ride about a spark plug gap away from the spinning impeller vanes on the pump. From what I have read, anything over .060" is giving up water pump efficiency. The solution is crude, the plate is kinda dished there and you just mash it flatter as evenly as possible until you have an improved but safe clearance. Don't want it to ever rub!"Do you mean the radiator cap for the pressure release?" Yes, folks often overlook the cap. It has two seals."Any ideas on how to diagnose this?" I found out when I pulled the heads. Shadowy areas on thrust side of the rear 3 cylinders of the right bank of a 73-4 400 block that had been bored .060 during a rebuild, and had over 50K miles on it since. I had just plopped better heads on it but had problems shortly after. I was blowing plenty of cylinder pressure into the cooling system. The shadowy areas of the cylinder walls were the beginnings of seeing thru to the coolant jacket, apparently. Or just porous areas in that particular casting, each is unique in that aspect. Sleeves would fix it but I overheated the thing so bad to get home that I called the block scrap, probably no longer square. Lets just say this is not your trouble, you would have combustion gas in the cooling system.
why the top end rebuilt? are they the same heads you had?was the water pump and new radiator an atemped to fix the heating problem?how does it run now?were the sleeves and o-rings behind the divider plate in good shape?what do your plugs look like? a lean engine will run hot.
76 455/4spd TRANS AM69 GRAND PRIX 455/5SPD
One thing that comes to mind we haven't touched on yet is the carb. When you performed the top end over haul, did you rebuild the carb? Or is it the same as before the temp issues? reason I ask is if you run too lean it will definitely cause the motor to run hot. can make as much as 20-30 degrees or more difference in motor temp.
Just curious if you took the tstat out and checked the flow as I did that on my 66 with a Flowkooler pump at about 50th and found a lot of flow. Also I didn't see any points on the air dam for air flow
First things first, determine if the engine is getting to hot, next fix the electrical problem that I do suspect you have due to a bad ground.Always get the low hanging fruit first. The carb would be next, as suggested, if it's running lean, it will run hotter. Pull any or all the spark plugs and look at the color of the electrode end, black is rich (too much fuel), white is lean ( not enough fuel) light chocolate is perfect. The electric fan could have an effect while going down the highway, sometimes they can block more air than they can move.For instance, lets say a fan can move 1000 CFM but the radiator can flow 3000 CFM.Fans become useless at high speeds including the ones mounted to the engine, due to the static air forced in through the grill the fan is not needed, that's why a clutch was added to help on fuel after flex fans where tried back in the 70s, they where designed to flatten out at higher RPM, they also robbed horsepower, the electric fans work great at idle speeds, with the relay and thermostat control, it will turn off at highway speeds.The crank timing would be the last thing to look at, if your not confident with doing this kind of work, get someone that can help. You may not understand some of the terms I have used. A chamfer is the flat area that is cut on a corner to remove the corner, the radius is the half round part cut on the shaft to prevent it from breaking. The chamfer is cut on the gear to prevent it from hitting the radius so the gear will rest flat against the shoulder on the crank. The gears only have a large chamfer cut on one side.Remember, first things first and don't give up.
Thanks everyone, here is the latest on the cooling problems.1. I swapped out the water pump divider plate, which had a hole drilled into it by the builder who did the top end. I didn't know about it until I searched through some emails from him that suggested drilling it. He referred to it as a "steam relief".2. I discovered that there was a bad ground. This explains the voltage fluctuations, and now that it has a solid ground, the voltage reads at 14 solid, then 13.8 when the fans kick in.3. I had a fan relay installed so the fans kick on after the engine warms up. This isn't working properly yet, so the car is back in the shop.4. I bought a mechanical gauge and installed it. Unfortunately, I couldn't keep in the old sensor due to lack of room.I put the car through the "torture test", which is taking it on a specific run on the highway where it always overheated. It stayed at 180-190 solid. I went an extra 5 miles up that highway, and it was rock solid. The sad reality is that it's been 4 years of chasing this problem. I'm both ecstatic to have solved it, while at the same time really bummed that I wasted so much time. I should have gotten on here a lot sooner.Since I changed so many things, it's hard to say whether the cooling problem did not exist or if it was solved by changing the water pump divider plate.I took the car out the next day and something happened in the electrical system and it's not getting any spark now. So, it's back in the shop to get sorted out. Next I need to replace the water temp gauge in the cluster. Does anyone know if it's possible to get an entire cluster replacement?